Suppression of biquadratic coupling at the Cr Néel temperature in Fe/Cr(001) superlattices (invited) (abstract)

We present the effects of antiferromagnetic (AF) order of the Cr spacers in Fe/Cr(001) superlattices on the interlayer coupling of the Fe layers. AF order of the Cr spacers is suppressed for layer thicknesses less than 42 Å. For .42 Å of Cr, the Néel temperature (TN) increases rapidly and asymptotically approaches the bulk value for thick Cr spacers as characterized by a transition-temperature shift exponent λ=1.4 ±0.3. Neutron diffraction confirms both the AF order of the Cr layers in superlattices with 62, 100, and 200 Å thick Cr layers, and the existence of the incommensurate, transverse spin-density-wave magnetic structure whose nesting wave vector is equal to that of bulk Cr. The AF ordering of the Cr results in anomalies in a variety of magnetic properties, including the interlayer coupling, remanent magnetization, coercivity, and magnetoresistance. Most strikingly, the 90° or ‘‘biquadratic’’ coupling of the Fe layers observed for T>TN is suppressed below TN as confirmed by polarized neutron reflectivity. This behavior can be understood in terms of the combination of finite-size and spin frustration effects at rough Fe/Cr interfaces.